Gage control for rolling mills



Dec. 29, 1970 j MKEL 3,550,413

GAGE CONTROL FOR ROLLING MILLS Filed July 16. 1965 A TTOR/VEY UnitedStates Patent 0 3,550,413 GAGE CONTROL FOR ROLLING MILLS Peter J.Barnikel, New London, Conn., assignor to General Dynamics Corporation,New York, N.Y., a corporation of Delaware Filed July 16, 1965, Ser. No.472,583 Int. Cl. B21b 37/12 US. Cl. 72--8 3 Claims ABSTRACT OF THEDISCLOSURE In the particular embodiment of the invention describedherein, a rolling mill includes hydraulic pistons applying a forcetending to urge the backup roll bearing chocks apart in parallel withthe separating force exerted by the material being rolled. A forcedetector interposed between the chocks and the mill frame detects thetotal roll separating force and another gage responds to the pressureapplied to the hydraulic actuators. A control system responsive to thesecomponents causes the pressure applied to the hydraulic pistons to varyin the opposite manner from the total force thereby tending to maintainthe separating force constant.

The present invention relates to an arrangement for shaping metals byrolling, and more particularly, to a novel and improved arrangement forproducing a constant thickness output product from a rolling mill standirrespective of thickness, temperature, or metallurgical properties ofthe incoming product or strip.

A conventional rolling mill stand generally includes two work rollswhich, by rotating in opposite directions, seize or grasp the metal anddraw it through the rolls reducing its thickness and increasing itslength. It also in cludes a mill housing which constrains the separatingforces imparted to the rolls by the metal being rolled, and a means ofadjusting the separation of the work rolls within the mill housing. Incommercial usage, various types of mill stands are employed whichutilize different numbers and combinations of rolls depending upon thetype of metal, width of the product being rolled, amount of reductionrequired, and other factors such as quantity of production. Before therolling process commences, the two work rolls are adjusted so that theirseparation or gap is equal to the thickness of the desired outputproduct less the stretching and bending of the mill stand which resultfrom the reaction to the roll separating forces developed during therolling process.

After the no-load adjustment or preset of the roll separation, if therewere no variations in thickness, temperature, or metallurgicalproperties of the incoming metal, strip, or sheet, then the thickness ofthe output product would be uniform. Inasmuch as the properties of theincoming product do vary and cause changes in the stand separatingforces, variations in the thickness of the output product result.

The above-mentioned problem is, of course, not new in the art andvarious attempts have been made to compensate for the characteristics ofthe incoming product to thereby maintain a uniform output thickness.

The most common approach has been to attempt to provide an automaticmeans of adjusting the roll separation during the rolling process tocompensate for the effects of stand stretch introduced by variations inthe incoming product. One common arrangement used is to employ anadjustment screw, the tightening or loosening of Adjustment screws aregenerally controlled in their operation by screw drive motors which aresupplemented by sophisticated motor controls. These motor controls may,in turn, be controlled by a plurality of gages measuring the variousphysical characteristics of the product entering or leaving the millstand. Objections to such a system are generally raised on the groundsof high costs and substantial adjustment time lags due to the inertia ofthe screw mechanism and of the motor controlling the screws.

Adjustment means are also known which act on the rolls independently ofthe adjustment screws, such as hydraulic actuation of the nut associatedwith the adjustment screws, the introduction of wedge actuators betweenthe adjustment screws and the roll chocks, and the substitution ofhydraulic rams for the adjustment screws to adjust roll separation.While these adjustment means, in some instances, overcome the objectionsto the use of motor controlled adjustment screws, they must be powerfulenough to act against the total roll separating force and areobjectionable in many instances because of their cost or difficulty inexecution.

Accordingly, it is an object of the present invention to provide a newand improved system for maintaining the working roll separation duringthe operation of a rolling mill which overcomes the above-mentioneddisadvantages of the prior art.

Another object of the invention. is to provide a new and improved systemwhich responds rapidly enough to permit complete automatic gageregulation of the material being rolled in a single mill stand.

A further object of the invention is to provide an adjustment systemwhich is simple and efficient in operation, may be installed easily inconventional rolling mill stands, and is capable of providing a highlyaccurate adjustment to maintain the roll separation gap.

Another object of the present invention is to provide a new and improvedmethod for maintaining in uniform fashion the output product of arolling mill.

An additional object of this invention is to provide an arrangementwherein relatively high force actuator devices are provided which tendto urge the rolls apart thus coacting with the separating force impartedby the metal being rolled in opposition to the constraining forces ofthe mill housing. By being responsive to a control signal, the actuatorscan rapidly compensate for variations in the incoming product tomaintain a uniform thickness in the output product of the mill stand.

These and other objects of the invention are obtained by providing, in arolling mill having a fixed frame and a pair of work rolls, one of whichmay be adjustable to the other to vary the roll separation, a pluralityof actuator devices acting in parallel with the roll separating forcesimparted by the metal being rolled and in opposition to the constrainingaction of the mill stand. By varying in a controlled manner the forcesapplied by these actuators, the forces applied by the work rolls to theproduct being rolled can be adjusted so as to maintain a uniform outputproduct.

More particularly, the no-load roll gap is preset with the adjustingscrews to provide a greater than normal reduction in the thickness of aproduct of predetermined properties, and thereafter the actuators areadjusted to stretch the mill stand and thereby achieve normal reductionof such a rolled product. Adjustment of the actuators therefore needonly be made about this level, and inasmuch as the actuator forces actin parallel with the mill stand separating forces produced by the strippassing the work rolls, the maximum actuator force need only be as greatas the maximum force perturbation range required to correct forvariations in the incoming product.

It has been found that the adjustment force can be obtained from thesolution of the following equation:

wherein M and M are the elastic moduli of the mill stand, neglecting theeffect of the rolls, and mill rolls respectively, and wherein AF is thevariation or differential in force constrained in the mill standhousing, and AF is the variation or differential in force applied by theactuators.

The solution of the above equation may be accomplished by utilizing aload cell for sensing the variations in the force (F), constrained inthe mill stand housing, and applying a signal representative thereof toa system which solves the above equation and adjusts the actuatorsaccordingly.

Further objects and advantages of the invention will be apparent from areading of the following description in conjunction with theaccompanying drawings, in which:

FIG. 1 is a side view of a typical rolling mill stand provided withcontrol actuators and with a repre entative system for controlling theactuators; and

FIG. 2 is a partially broken-away view taken along line 22 of FIG. 1.

In a typical four-high rolling mill, wherein the present invention maybe practiced, a rolling mill stand includes a rigid housing 11 in whichis mounted a roll assembly having a plurality of rolls mounted aboutsubstantially parallel axes including a lower backup roll 12, a lowerworking roll 13, an upper working roll 14, and an upper backup roll 15,all of the usual type. Within each side of the housing 11 the lowerbackup roll 12 is supported in a lower bearing chock 16, and each sideof the lower working roll 13 is supported and guided in a smallerbearing chock (not shown) which in a conventional manner fits into acorresponding opening in the chock 16. Simi larly, at each end of thehousing 11, the upper backup roll 15 is supported in a bearing chock 18and each side of the upper working roll 14 is guided by a small bearingchock (not shown) which is received in a corresponding opening in achock 18, each of the backup roll bearing chocks being mounted forvertical sliding motion in the usual manner so as to permit adjustmentof the working roll separation.

As in conventional mill stands, an electric screwdown system 26 ismounted at the top of the housing 11 in order to make any large scaleseparation adjustment which may be necessary before or between milloperations. This system includes the usual drive motor 21 along with areduction gear system 22 and adjustment screws 24 which bear through abreaker block-load cell assembly 44 upon the bearing chock 18. As bestseen in FIG. 2, the upper and lower chocks 16 and 18 are separated byhigh force adjustment actuator devices 27. These actuator devices 27operate so as to oppose the constraining forces of the mill housing onthe chocks 16 and 18 and are adapted to apply force differentials uponthe chocks 16 and 18 in order to maintain uniformly the output productthickness of the mill stand 10.

The compressive forces exerted by the work rolls 13 and 14 upon thestrip or work product are transmitted by the adjustment screws 24through the breaker blockload cell assembly 44, upper bearing chock 18,upper backup roll 15, and upper work roll 14 to the strip and throughthe housing 11 by way of nut 30 to the rocker plate 31, lower bearingchock 16, lower backup roll 12, and lower work roll 13 to the strip.

In the practice of the invention, the no-load gap or work rollseparation is initially set by means of adjustment screws 24 to providea greater than normal reduction in the thickness of a product ofpredetermined properties. Thereafter, the mill stand 10 is prestressedby means of force actuators 27 to achieve a normal reduction in such aproduct. It is possible to make perturbation adjustments in accordancewith commands from an OLIlJSluC 4 source so as to maintain the work rollseparation and thereby provide an output of uniform thickness from millstand 10 irrespective of changes in the product.

The following analysis is directed to the development of an equation,which when the actuators 27 respond in accordance therewith, can enablemill stand 10 to provide a work product of constant output thicknessregardless of the variations in the incoming temperature, thickness ormetallurgical property of the metal product being rolled from thepredetermined properties.

The preset roll separation (S) of the mill stand 10, as initiallyadjusted and measured by means of adjustment screws 24 to produce anoutput product with a desired thickness h, can be expressed in terms ofHookes Law by an equation of the form:

wherein M is the elastic modulus of the mill stand, neglecting theeffects of the mill rolls, and M is the elastic modulus of the millrolls.

When the incoming product varies in a manner to cause a change in thestand separating force (AP) which causes variations in the thickness ofthe output product (Ah), the effect may be described in the followingman ner by transposing terms and substituting in Equation 2:

21 P-l-AP P-l-AP S M, M. ME

Inasmuch as the thickness of the output product h is to be kept to auniform dimension, Ah must be reduced to zero, which can be accomplishedby varying the value of F Theerfore, by inspection of Equation 3 itfollows that:

+ I i 11 'i =h (a. constant) wherein, as stated, F is the initial force(chosen at a value which will permit a satisfactory range of adjustment)applied by the actuators 27. The position of adjustment screws 24 iskept constant such that S is a con stant. Therefore:

and

manqu From FIG. 2 it is apparent that:

2F=2F +P and 2AF=2AF +AP wherein F equals F -I-AF and F is the forceconstrained at any time in the mill stand housing and equals (F +AF)where F is a selected initial or reference value for F. Thereforesolving for AP:

AP=2(AFAF (6) and substituting for AP in Equation 5 and solving for AFThe significance of expression (7) is that it relates the change AF(from value F which is induced at any time in the mill stand force F tothe change AF (from value F needed to be made at that time in theactuator force F in order to maintain the output product thickness ofthe desired value It or to restore such thickness to that value h.

The actuators 27 located between bearing chocks 16 and 18 are shown inthis embodiment as hydraulic cylinders provided with fluid lines 35 and36 for delivering from a unit 40 a supply of hydraulic fluid originallyderived from a source of pressurized fluid (not shown). The fluid flowand pressure in the lines 35 and 36 are controlled by the hydrauliccontrol unit 40 which con tains a conventional electro-hydraulic servovalve such as Model 324 manufactured by Sanders Associates, a transducerfor sensing pressure in the actuators such as Model PG707TC manufacturedby Statham Corporation (said pressure being a measure of the force Fexerted by the actuators); and the usual manifold, stop valves, checkvalves, and filters. The unit 40 is responsive to a control signalproduced by amplifier 41 to adjust the force F exerted by the actuators27.

In order to apply the above derived Equation 7 to control the forcedifferential AF exerted by the actuator devices 27, a representativecontrol system has been set forth in FIG. 1. The various components ofthis system are shown in their inactive or deenergized condition. Inoperation, the mill adjustment screws are preset in accordance with therolling schedule. Prior to threading the strip into the mill, contacts1R-1 of relay 1R maintain the output of an integrator circuit 42 at 0volt. Also, the contacts 3R-3 of relay 3R ground the shown AF input toerror sensing difference amplifier 41 to maintain that input at 0 volt.

When the product begins to thread between the work rolls 13 and 14, theforce (F) constrained by the mill housing 11 increases and is measuredby a conventional load cell (not shown) in breaker block-load cellassembly 44, the cell providing an input to an amplifier 45. The otherinput to amplifier 45 is supplied from an adjustable voltage source 45aand is representative of the initial force F exerted by the actuators 27upon the chocks 16 and 18. Source 45a may be adjusted in ac cordancewith an indication derived from unit 40 of the force F to provide asignal F of the proper value. As represented by its negative sign, thesignal P is in voltage opposition to the signal representative of theforce F.

In operation, as the strip threads between the work rolls 13 and 14 andthe force F increases to increase in a positive direction the value ofthe combined signal input (F-F to amplifier 45, that amplifier isadapted to provide a negative output voltage of increasing magnitudesuch that, when the output reaches a predetermined magnitude equal to apositive bias level set into a signal comparator 1SC, the comparator 1SCenergizes and closes its contacts 1SC-1 which energize relays IR and 2R.Relay 1R, thereafter, opens its contacts 1R-1 to remove the short acrossthe integrating capacitor 42a of the integrator 42. At the same time,relay 1R closes its contacts lR-Z and 1R-3 to complete circuits to bothof two inputs to an amplifier 46. Relay 2R is an adjustable time delayrelay to permit selection of the time of actiavtion of the system afterthe metal has entered the mill stand.

The output of integrator 42 is connected to an amplifier 47 of whichpart of the output is fed back'through lead 47a through contacts 1R-3 toone of the inputs of amplifier 46. Amplifiers 46 and 47, in combinationwith the integrator 42, thus form a closed loop circuit adapted todevelop at the output of amplifier 47 a signal which is representativeof a fixed reference value for the force F. Such reference value isdesignated as F and is used to permit the continuous solution ofEquation 7 while the total length of strip is being rolled.

When signal F is equal in magnitude to the signal P, a signal comparator2SC is energized and closes its contacts 2SC1, which causes relay 3R tobe energized when the time-delayed contacts ZR-l close. Relay 3R thenopens its contacts 3R-4 to lock in the value of F produced by theintegrator 42 and, at the same time, opens its contacts 3R-3 to removethe short to ground for the AF input to the amplifier 41. Relay 3R alsocloses its contacts 3R-1 and 3R-2 to permit the signal F and the signalrepresentative of the force F to be supplied to the shown amplifier 48.

The amplifier 48 operates to subtract F from F and provides an outputrepresentative of AF to amplifier 49. The output of amplifier 49 issupplied to a coeflicient potentiometer 51 which, in effect, multipliesthat output The output of unit 51 is in turn fed back through amplifier50 to the input of amplifier 49. By standard operational amplifiertechniques the circuit 49, 51, 50 solves the foregoing expression (7) toyield at the output of element 51 a signal AF representative of the lefthand term AF of that expression. As stated, AF is the change needed(from F in the actuator force F in order to maintain the output productthickness of the desired Value h.

The amplifier 41 has supplied thereto three inputs, the first suppliedover lead 52 from unit 40 and representative of the force P the secondfrom source 45:: and representative of F and the third from element 51and representative of -AF,,. Amplifier 41 sums those three inputs tosupply over lead 53 to control unit 40 an error signal E which is afunction of the quantity (F F AF The primary function of amplifier 41 isto control unit 40 so as to maintain the total actuator force E at thevalue F t-AF needed to yield the desired value h for the output productthickness. By performing that function by means of the shown closed loopconnected of units 40 and 41 (wherein the signal F is derived from unit40 and fed back to unit 41), the additional advantage is realized thatthe actual value P of the actuator force is prevented by the closed loopcircuit from departing significantly from the value F -I-AF commandedfor that force.

In operation, the system shown in FIG. 1 is arranged to rapidly adjustfor variations in the incoming product by solving Equation 7 and, inaccordance therewith, by varying the force exerted by the actuators 27(acting in unison) to maintain a uniform output product. It is to beparticularly noted that the present invention does not require the useof any gages to measure the product entering and leaving the mill stand10.

It will be understood by those skilled in the art that theabove-described embodiment is meant to "be merely exemplary in that itis susceptible to modification and variation without departing from thespirit and scope of the invention. For example, the invention has beenillustrated in regard to a four-high rolling mill, but its applicabilitywith other types of mill stands will be readily appreciated to thoseskilled in the art.

Further, the signal AF can be derived from circuits simulating theexpression:

which is equivalent to the foregoing expression (7). Still further, theshown closed loop of units 40 and 41 can be replaced by an open loopconnection wherein the signal supplied over lead 53 is proportional tothe desired total actuator force (F -PAR and commands the control unit40 to cause each actuator 27 to yield that force.

Therefore, all such variations and modifications are included within thescope of the invention as set forth in the appended claims.

I claim:

1. In a rolling mill having a plurality of rolls rotatively mountedabout substantially parallel axes, bearing means for supporting therolls, means supporting the bearing means for constraining theseparating force imparted to the rolls by the product being rolled,means mounted on the supporting means and acting on at least one roll toset the separation between the rolls, adjustable actuator means actingon the bearing means to apply a force which coacts with the separatingforce to oppose the force constrained by the supporting means, theactuating means including means responsive to a control signal to varythe force applied thereby, the control signal being a function of theforce constained by the supporting means to maintain the work rollseparation, wherein the varying force AF applied by the adjustableactuating means satisfies the relationship:

wherein AF is the differential in force constrained by the supportingmeans and M and M are, respectively, the elastic modulus of the millrolls and the elastic modulus of the mill stand neglecting the effectsof the mill rolls.

2. In a rolling mill as in claim 1 wherein the actuator varying meansincludes high force hydraulic actuators, a source of pressurized fluid,and system means for controlling the pressure of the fluid admitted tothe actuators.

3. In a four-high rolling mill for producing a product of substantiallyuniform output thickness having a fixed housing, a roll assemblyincluding upper work and backup rolls, lower work and backup rolls, allof the assembly rolls mounted about substantially parallel axes, upperbearing means mounted on the housing for supporting the upper rolls,lower bearing means mounted on the housing for supporting the lowerrolls, means mounted on the housing and acting on at least one roll toset the separation between the work rolls, a plurality of high forceactu ators each acting in unison on the upper and lower bearing means toprovide a force thereon, and means for varying the force applied by theactuators to satisfy the relationship:

AFC: (AFCAF) (1+5?) wherein AF is the differential in force constainedby the housing and M and M are, respectively, the elastic modulus of themill rolls and the elastic modulus of the mill stand neglecting theefiects of the mill rolls.

References Cited UNITED STATES PATENTS 3,315,507 4/1967 Marten 72-163,398,559 8/1968 Tracy 728 1,935,091 11/1933 Iversen 72245 2,430,410 11/1947 Pauls 72245 2,525,687 10/1950 Kritschen 72248 2,903,926 9/1959Reichi 728 FOREIGN PATENTS 1,348,136 11/1963 France.

MILTON S. MEHR, Primary Examiner US. Cl. X.R. 72245

